Gas lift operation in a moving bed conversion of hydrocarbons



June 1955 J.-w. DELAPLAINE v 2, 1,

GAS LIFT OPERATION IN A MOVING BED CONVERSION OF HYDROCARBONS Filed April 17, 1951 RNE United States Patent GAS LIFT OPERATION IN A Movmonnn CONVERSION OF HYDROCARBONS John W. Delaplaine, Swarthmore,

Process Corporation, of Delaware Pa., assignor to Houdry Wilmington, Del., a corporation Application April 17, 1951, Serial No. 221,405

6 Claims. (Cl. 196-52) The present invention relates, in general, to the operation of systems for elevating granular material through an upright conduit, such as a liftpipe,'by-.means of a gas stream, and is particularlydirected to, a method for effecting elevation of granular material by ;the lift gas under conditions obtaining high efiiciency andreduced attrition of the granular material. Although not limited thereto, the invention finds important application in the elevation of a granular contact mass,jsuch as catalyst, in

fluid density'varies, directlywith the pressure of th'e "gas,

- Effortsto reduce the extent of accelerationof catalyst instance by uniformly tapering-the 1 in the direction of travel: of the?" a hydrocarbon conversion system, wherein the contact mass is continuously circulated througha .downfiow path comprising one or more processing zones and is thereafter returned to the top of said path by a gas lift. 1

Granular contact material, such as, catalyst, which may be in the form of cylindrical pellets or substantially spherical beads, is subject to attrition by impact. and abrasion, and because the material is in continuous c1r culation, the formation of a large quantity of finesas result of such attrition presents a major problem.

Since the efii'cient handling of hydrocarbon conversion 1 catalyst is a principal object of the invention,- in the description which follows this material is specifically referred to as typical, butit will be understood'that the.

invention is not limited thereto.

in the moving bed type of hydrocarbon conversion process, relatively large particles or granules, such as sized pieces, pellets-formed spheres and the llke ranging in size from about 0.05 to 0.5 inch in diameter flow.

principally or solely, underv the infiuence' of gravity through a downilow path or paths of a system 1n wh1ch there are one or more processing zones wherein the granular solids are'contacted with fluids which are con verted by contact withthe granular solids and/or which are utilized in treating the granular solids. The grav tational fiow of solids through such processing 'or. treating zones is principally or solely as compact downwardly v moving non-turbulent beds. Such systems are discussed generally in The T. C. C. catalytic cracking process for.

motor gasoline production by R. H. Newton, G. S. Dunham, and T. P. Simpson, Transactions ofthe American Institute of Chemical Engineers, volume 41, page 215, April 25, 1945, and the articles there cited.

In such a moving bed type of system, it has been found advantageous to transport the solid particles (i. e., catalyst or other contact material) by oneor more pneumatic or gas lifts which serve as an upiiow path or paths. The system may comprise a single downflowpath' iniwhich there are several, process zones at 'diiferent heights through which zones the contact material flows consecutively so that the solid particles need be transported by the gas lift only once in a complete cycle of operation or the system may comprise a plurality of gas lifts and/or downfiow paths each containing a'single process zone.

An exemplary system of the former type has been described in an article entitled Houdriflow: new design in catalytic cracking, appearing in the Oil and Gas Journal, page 78, January 13, 1949.

When catalyst is introduced into the gas stream at the reaches, or more accurately,

' conduit. Accor'dingly,

exchange between catalyst and gas the catalyst is moved through, the lift pathwithprogressively:increased veloca height-required in Comn'iercial practice, fairly high linear velocities may be reached A under normal operating conditions in' liftingfsolid ,g'ran 1 catalyst, of. the size range herein iry, so that in lifts of 7 lift conduit outwardly .by-the use of the hotter'gasinaccordance sequent increase'in gas velocity accompanied bottom of a lift, the transfer. of momentum from the fluid to the catalyst is not .instantaneousif 'A certain.

by. the catalyst before it l closely approaches its equi-f libriurnvelocity which is attained when theonly remainportion of thelift is traversed fling driving force foracceleration of the catalyst'is'-'that-;

due to changing static pressure with lift height. Since the:

it will be seen, that. as the gas pressure; decreasesithe linear velocity of .the fluid is correspondingly increased causing a further .a cceleration oftthejcatalyst ;in the lift even in the absence of heat ular particles such as V contemplated. At high catalyst; velocities, it has' been found in practice, increased catalyst "attrition results.-

inthe lift conduit, for

catalysthave not met with the expected success and in L.

many instances 'erratic operation resulte'dla's opposedqto desired substantially smooth straightlineflowthatycan beobtainedina liftconduit of substantially uniform diameter. i

-"ljhe total'pre'ssure,drop required to producea certain catalyst circulation at a given rate of fluidyintroduction Acan bemathematically predicted. The'p'res's'ur'e drop eliiciency of a particular lift system. is the quotientofQ I the calculated lift I pressure drop obtained in operation of the'lift; :"Since, u)-

pressure drop divided by the. actual in most commercial units the desired conditions are l close to the maximumavailablepressureandmaximum allow? Y able catalyst veloci'y, when lower? than normal efiiciency, is encountered on thebasis of A tions, it means that the'lift catalyst'at a rate materially belo'w calculated design and pressure drop considera; is operating to circulate! expectation; Low .lift pressure efliciency, moreover, is

often indicative of unsteady or. erratic flow atone or more regions along the lift-path, which may be a inajor cause of abnormalcatalyst attrition. I It will b'e seen, therefore, that raising the gas inlet pressure does not afford V a practical1solution to' the problem, even' tendency for occurrence of regions of unstable flow 'Withinthelift. e

While heat transfer betweentransporting gas and gran. ular material having a temperature differential therebetween is quite rapid, it is not instantaneous. Precise mathematical calculations of the rate of'incremental heat transfer along the lift path cannot be made "on the basis t of concepts developed from fundamental studies of heat) transfer relationships in fluid dynamics in view of the paucity of reliable information on the behavior'of such 7 systems, but empirical data obtained inthedevelopment littered-Jamal.

if this were possible 'and'were not otherwise economicallyprohibitive.

It has now'beenfound that improved lift operating efficiency is obtained by theuseoflift'gas zone of initialv engagement therewith-is atta temperature the catalyst, I

of the present invention are adequate for all practical purposes in establishing the operative conditions and techniques for commercial adaptation of the invention.

The invention will be understood from the detailed description which follows read in connection with the accompanying drawings illustrating schematically in Figures l and 3 embodiments of typical systems to which the invention applies; Figure 2 is a partial view illustrating one form of heater that may be used for heating the lift gas.

Referring now particularly to Figure 1 there is shown a typical system suitable for use in hydrocarbon conversion operations, such as cracking, in contacting fluids with granular solid materials, of the type employing compact gravitating beds of such granular materials in the fluid contacting zones. The system comprises principally a convertor vessel or reactor indicated generally at through which the solid contact material flows as a downwardly moving non-turbulent bed, and is transferred through a conduit 11 to a regencrator vessel or kiln indicated generally at 12, in which the carbonaceous deposit formed on the solid material in the reactor, is removed. The granular material may be an inert substance utilized for its heat transfer capacity, but in the more general case the granular material is catalytic in nature. Compositions effective as hydrocarbon conversion and/or cracking catalysts (typically natural or synthetic aluminosilicate) and the conditions employed for conversion of hydrocarbons in reactor it! and for regeneration of the catalyst in kiln 12 are Well known to the art and need not be repeated here.

Regenerated catalyst particles are withdrawn from kiln 12 and flow downwardly in conduit 13 as a compact nonturbulent column to a gas lift engager or transfer chamber, indicated generally at 14, from which the catalyst is lifted and transported vertically upward as a continuous stream of solid particles by a transporting or lifting gas introduced into the transfer hopper 14.

Under the impelling influence of the lifting gas, the.

catalyst is introduced into and transported through the lift conduit 15, which extends from within the transfer hopper 14 and upwardly through the top thereof to a point of discharge at an elevation above that of reactor 10. The catalyst is discharged from conduit 15 into an enlarged separating or disengaging chamber 16, where as a result of the expanded area, the catalyst separates out from the gas stream and drops to the bottom of the chamberv From the chamber 16 the catalyst is withdrawn by a conduit 17 for return directly to the top of reactor 10; or if desired, the catalyst may be sent to an intermediate surge hopper supplying that reactor.

In the embodiment illustrated in Fig. l, the catalyst entering the hopper 14 assumes an angle of repose as shown at 18, constituting the top level of the bed of catalyst accumulated in that hopper. Lift conduit 15 extends downwardly into the hopper 14 to a level below that of the catalyst therein. A sleeve 19 surrounds the lift conduit within hopper 14 and extends downwardly into the hopper to approximately the same level as the bottom of the lift conduit 15. The sleeve 19 is closed at the top thereof and open at the bottom so as to form an annular gas-passing space 29 between the outside of the lift conduit and the internal wall of the sleeve. A gas supply line 21 is provided to supply gas to the annular space 2% for downward flow therein. An annular baflie member 22 is arranged within the hopper 14 inwardly from the wall thereof and at a level intermediate the top of the catalyst bed and the bottom of the lift conduit, so that catalyst flowing over the baffle will be directed outwardly at an angle at the inner edge of the baffle to provide a solids-free space or plenum below the bafile. A second gas supply line 23 communicates with the plenum under the baffle.

By the particular gas inlet arrangement above described, the rate of flow of solids into the lift conduit 15 can be readily controlled over a wide range. The lift operation is extremely sensitive to the flow of relatively minor quantities of gas in a direction concurrent to the lateral flow of solids toward the mouth of the lift pipe, so that by the introduction of relatively small quantities of lift gas through supply line 23, a substantial increase in the solids flow rate is obtained. In practice, the primary or principal quantity of lift gas, as about -70% or more of the total volume of lift gas introduced into the hopper 14, is supplied by line 21 through the sleeve 19, the remainder being supplied at least in part through line 23 as a secondary stream. If desired, secondary gas may be introduced through line 24 at the bottom of hopper 14, in lieu of or in addition to that introduced through line 23. The outlet of line 24 is surmounted by a cap. or screen 25 to prevent solids from falling into thatline during periods when gas flow therethrough may be cut off. The stream of lift gas discharged through line 24 is directed upwardly toward the mouth of the lift pipe, which is separated from the discharge outlet of line 24 by a gap of sufiicient vertical height to permit the formation of a relatively static layer of solids between the bottom of the lift and the outlet of pipe 24. Within this relatively static layer, there is no substantial lateral movement of the solid particles, although portions thereof may continuously pass upwardly out of the layer into the stream of primary gas discharged through the sleeve and enter therewith into the lift conduit 15, being replaced in the bed by downwardly moving solids. For a given quantity of lift gas, control of the solids flow rate is obtained by dividing the total flow of lift gas between the primary stream introducedthrough sleeve 19 and the secondary stream or streams introduced through line 23 or 24, or both. These various streams of gas may be the same or different in kind.

In operation of the system thus far described, the catalyst gravitating through the reactor 16 is contacted with hydrocarbons, which may be supplied in vapor or mixed phase, or both. Thus, hydrocarbon vapors ma be supplied for concurrent flow through the reactor by a line 26 and reaction vapors removed from the bottom of the reactor by discharge line 27. To maintain desired pressure differential between the disengaging chamber 16 and reactor 10, seal gas is introduced into the column of catalyst flowing through conduit 17 as by means of a line 23 supplying steam or other inert gas above the reactor bed. Below the level of withdrawal of the hydrocarbon reaction vapors from reactor 10, a purge zone is provided, into which steam or other inert gas is introduced through a line 29 communicating with the zone.

The spent catalyst discharged from reactor 10 into the regenerator 12 through seal conduit 11, is contacted with oxygen-containing gas in the regenerator to burn off combustible deposit. In the embodiment diagrammatically represented in Figure l, for instance, the oxygen-containing gas is introduced into the regenerator by lines 30 and 31 and combustion products in the form of flue gas re moved therefrom by lines 32 and 33.

In practice of the invention there is no particular limitation as to thekind of gas or vapor that can be employed as lifting medium. Conveniently flue gas discharged from the kiln 12 or from a selected zone thereof may be sent to the transfer hopper 14' for use as lift gas therein, and the flue gas may be supplemented by steam or other inert or compatible gas from other sources.

In certain cases it may be preferred to operate with. cross flow gas introduced through line 23 instead of diffuser gas supplied through line 24 as the secondary gas supply; however, by their joint use the range of flexibility and control is beneficially extended.

Where gas from an independent source is employed as lift gas, it will be understood, that gas may be heated to any desired temperature above that of the catalyst, in practice of the invention. from kiln 12 as the lift medium, ordinarily, such gas. wfll In using flue gas discharged not have the desired temperature higher (than that of the catalyst discharged from the kiln and admitted to the transfer hopper 14. In order to obtain the desired high temperature in the lift gasfor practice of the present invention, suitable arrangements will ordinarilybe necessary for raising the temperature of'the flue-gas to that required. A convenientmethod and device for heating the flue gas to the desired. temperature is'by the use of an air-line burner such as diagrammatically; illustrated in Figure 2. A suitable gaseous fuel, such as propane,

is ignited and burned at the tip of a jet'34 within an enclosed housing 35, and in an atmosphere of air supplied. through a pipe 36 surrounding the jet. A cylindrical par-- tition 37 extends partway up into the housing 35 and is spaced from the wall-thereof to provide the boundaries for a combustion chamber 37a which is open at the top. Flue gas to beiheated isadmitted through a conduit 38 communicating with the space between the partition 37 and the wall of housing 351 In operation, the hot combustion products and heated air from .the combustion chamber 37a rise to the top of housingSS and are ad mixed above the partition 37 with the flue gas toprovide a substantially inert hot gas mixture discharged at the top of housing 35 through conduit 39, which may be en ployed as lift gas.

a final gas mixture at the desired temperature.

Alternatively the flue gas can be heated by oxidation of CO and other burnable material present therein, taking, advantage of the exothermic reaction to raise the 'ifii'lk perature of that gas. .As disclosed in prior "U; St patent of Eugene J. Houdry, 2,248,994 of July 15, 1941, such oxidation may be efiected-by addition of an oxidizing medium such as air or by passage of the line gas over oxygen-supplying catalytic materials As therein d The quantity of air supplied to the burner may be regulated'so that there is no substantial excess of free oxygen in the gaseous products discharged; through conduit 39 and the relative proportionof iiue gas admitted through'line 38 can be controlledto provide 1 thermo compressor.

closed the gas may be passed over CuO to effect the dc-S sired oxidation. Increasein temperatureof 200400;" or more can be thus eilected.

In the use of flue gas as lifting medium, even if suit-. able arrangements are made for utilization of such gasdischarged from a selected region of the him at relatively high pressure, it is not always desirable or convenient to operate the kiln at pressures affording flue jgas 'a-t the required pressure for use as lift gas. ,Ithas accordingly been proposed, for instance, in copending applicationof 3 George D. Myers, Serial No. 124,293, filed October 29, i

1949, to raise the pressure of line gas for use as' lift'gasby injecting high velocity steam at higher pressure into the flue gas. In doing so, itwill be understood, that unless I the steam is supplied at a temperature substantially equal to that of the flue gas (or higher), there will be a result'-' ing cooling of the'flue gas ,by the cooler steam'injected' therein. The practice of the present invention is particularly advantageous in heating up cooled flue gas-steam mixtures thus obtained, to avoid the detrimental eifects f otherwise encountered in using lift gas which is coolerthan the catalyst being lifted thereby. 'An arrangernent for the use of flue gas containing injected steam 'isillustrated in Figure 3 of the accompanying 'drawingsi;

Referring now to Figure 3, there is shownithesarne arrangement of reactor 10, kiln 12 andilift systemas heretofore described, said lift system cornprisingtransfer.

hopper 14, lift conduit. 15, and separatingehamber lo.

A somewhat modified construction of the kiln is shownin that the lower portionhas been flared outandincreased in diameter as indicated at 40. By this-construction the pressure of the flue, gas discharged from the lowermost combustion zone will be relatively higher for anyf'given gas inlet pressure as a rcsult'of the reduced height of the bed in such lower Zone for a particular bed volume.

Regeneration is effected as in the previous embodiment in two series of vertically superimposed adjacent. re-

' furnish flue gasfor .use. as liftmedium. Thus'.,th;'fi1ie V l gas 'discharged through conduit 43xrnaybra substantially below,-'such;as fromi'10.-50% .of-the staticgas'lpressure at the bottomof the lifting zone inltransfefhopper 14 l Tofraisethe pressure of the flue gas, it .is'passed to a steam I jetthermo-cornpressor 46,-wherein thereis formed a than g pressure at the bottom of} the lifting f allowance, of course,: for any-pressure drop-,betweenfl'the thermo compressor andthe lifting zone. n

plishedfbyinjectin'ginto the stream offlue-gasfpassinga through thermocompres'sor dm .hi gh velocityfsteamiobtainedgby e panding-high;pressure steam, suchxa si'steam fyata pressure from dbOll-USQ to about 290 lbsl-persqu'are what above the catalystleveL plied :through line 42 passes into the ,top' of hopper portion ofzthe gas thus introduced.through'fline I pass down through the annuIars paceQSF betweenthesleeve" and; thefliftconduit; to jengagecatalys t therebelow and I elevate the-same into the lift'conduin Ajrninor portion p catalyst; 'outsideofi-the. sleeve 5 0;,and ftheninwardlybelow the 'sleevezintdthe' liftcondui I 7 controlled by valve 55.}: l 4 By injecting from ab0ut:.0.l I

poundpf. flue gas, depending on thespressurefthereof,51

the absolutepressure ofthe'flue'gas from-conduit 43iniay l 5 generation stages through which "the; atalyst 'containing' combustible deposit flows SuCCessively'. 'Iti-;will}be understood-"that if desired three ory m'ore of such egene'ration in the orderof Ll-0.2 lb. per square inch; The oxyge containing gas introduced by conduit .42 passes upwardly through the bed ofca talyst in the,upperlportionof the kilnfand resulting flue gas-is removed throughconduitAi In accordance'with this embodiment, theregeneration zone canbe operated at comparatively low pressureyet ture of, said flue gas and. "stea at? ofthe flue 'gas' alone and at least equa f inch, fromline '47 through' the nozzle of the steanr je thus formed is thereafter passed throu gh 'a suitable heater p hot gasfmixture issuppliedto transferhopper 14 into which'the'mixture' enters through i-su'pply line 49 and one orfn-iore branch: lines "communicating" with the U.= S. Patent No.12248;994;'hereinbeforereferredto; ,Althoughitwfll be uuderstoodthat1the'sarnelift hopper 1 I 4s. and the The heater; may be {of i a. design; described 'i arrangernentnn z y be; employed as that" illustrated inEFig'; l a modified embodiment thereof; isillustrated in" Fig;

an open endedisleeve 50Eentirely,within' the hopper, surroundingthe'liftpipdlSiand extending from-a level below thatofthe catalyst bed'in. the hopper tozaidistance some-' portion of. the gasfsupe by branch line 51fthrough'a' control; valve 1521-" Th ofth'egas will pass down through the fbedoifj v l 5, .Diffusergas ente bot-tom v'of hopper '14 and: b'elow themouth of the lit conduit through-the pipe 54 which --is'in"axial al merit with ;the 'li ftwbnduit; admission ofqigas into. pipe 54""8 be ra ofqthe latterito the {brine -In general the steam injeetedthrough1in 47 f x t f i j a temperature prrmmaboutfillof to 40Qi'E 1when usmg' ;,dry.saturated steam;.; .or' thejsteanr'maybesuperheated I in having a'press'ure higher hr zone, withQsliitablef.

"This is accom Instead of "a ,sleeve sealed off from th e solids free ,space v. x ahove i-the catalystbed' inthe hopper 14, asinfth'e previous 5 l embodiment, there is show'nwin,'the'present embodiment the I ed'to a {pressure in iconduit 49 such ith t "the :r'a'tio j 7 if desired, for instance to about 700-900 F.; the flue gas ordinarily ranges in temperature from about 900-1100 F.

In the event that the amount of flue gas discharged through line 43 is in excess of that required for lifting, a portion thereof may be withdrawn through branch line 57 under control of valve 58, serving to maintain a constant pressure in conduit 43. In this way only that amount of flue gas necessary for lifting is raised to required high pressure and the operations of regeneration and lifting are maintained independent of each other to afford increased flexibility to the system. Under control of valves 52 and 55, the amount of gas supplied respectively to lines 51 and 54 may be adjusted. In some instances it may be desired to permit a slight excess of the mixture of steam and flue gas to enter line 49, in which event such excess may be discharged through a bypass 59 under control of valve 60, which serves to maintain a constant pressure in conduit 49.

By supplying relatively cool air for regeneration through line 41, and with provision for indirect heat exchange in the lower zone of the kiln, the catalyst can be discharged at a temperature lower than that of the flue gas withdrawn through line 43. Thus, in a typical operation the catalyst enters transfer hopper 14 at about 900925 F. while the flue gas is withdrawn through line 43 at about 1000 F. If there is added per pound of flue gas in the thermo-compressor 0.5 pound of superheated steam at 800 F. the resulting compressed mixture of steam and flue gas will be at a temperature of about 875-900" F. This mixture can be heated to desired temperature in the manner already described.

To obtain the stated advantages of the present invention from the standpoint of improved lift pressure operating efficiency, the lift gas is to be employed at a temperature above that of the catalyst engaged thereby, significantly increased efficiency being realized when the catalyst is at a temperature of 800-1 100 F. and the lift gas is at a temperature of 100 F. or more above that of the catalyst. Best practical results are obtained in a lift of uniform cross section over at least the major part of its length, when the lift gas is a temperature of about 200350 higher than that of the catalyst. To obtain optimum conditions of completely uniform catalyst velocity over a distance of from about the 20 foot level to about the top of a 200 foot straight lift, the over-all temperature of the lift gas should drop approximately linearly in the order of about 400 F. The stated optimum can be achieved only by careful external control of heat transfer which renders such design and operation rather complicated and costly for ordinary commercial installations. Furthermore, if the lift gas temperature is more than about 400 F. above that of the catalyst, the rate of acceleration in the lower portion of the lift will be excessive and may be followed by undesired deceleration higher up in the lift, tending to produce regions of instability. However, the use of lift gas within the above indicated operating range of temperatures above that of the catalyst, can be readily obtained and the described practical advantages realized.

While in the preferred aspects of the invention it is recommended that the lift gas be introduced into the lift, at a temperature materially above that of the cata lyst, the invention is not intended to be limited thereby. If lift gas is conveniently available at required pressure, as in the case of the steam-flue gas mixture employed in the embodiment of Figure 3, but at a temperature below that of the catalyst, the lift gas may be heated to a tem perature equal to or not substantially above that of the catalyst. In thus using lift gas at approximately the temperature of the catalyst, the extremely low efliciency and poor lift operation that otherwise may result from the use of lift gas at a temperature lower than that of the catalyst, are avoided. Thus, it has been found that by using lift gas entering the lift engager at a temperature of Ull -400 F. lower than the catalyst temperature,

q z lift pressure drop efficiencies of only about two-thirds or less of the normal eificiency (at equal temperature) are obtained.

in lifting granular catalyst at 1050 F. with flue gas as lift medium at respectively: '(1) 750 F., (2) 1050 F., and (3) 1350 F., there is a significant difference in the velocity profiles of the catalyst, for the same catalyst mass circulation rate and the same final maximum atrained velocity. Thus, in plotting the respective catalyst velocity profiles at various points along the lift in each of the three cases, with distances above the lift in-- foot per second per foot of height in the case of gas a cooler than the catalyst.

In the elevation of granular contact mass such as catalyst by gas in lift conduits of commercially useful size,

a certain minimum gas velocity must be obtained to ef-i feet desired smooth flow; below such minimum velocity a condition of instability prevails which may be characterized by erraticpressures in the lift, slugging, turbulence, and other factors tending to cause excessive attrition of the solids. In order to minimize these conditions of instability in the lift, gas supply rates ordinarily have to be employed such as to obtain rapid acceleration of the solids to the minimum or critical velocity, obraining stable flow within a very short distance of travel in the lift; and in doing so, using the required amount of lift gas of comparative high fluid density, the acceleration of the solids is continuously augmented by the progressive reduction in fluid density which may lead to the attainment of undesirably high velocities at or below the discharge outlet of the lift. By the present invention, when using lift gas at a temperature higher than that of the catalyst, advantages are had of the increase in fluid density by loss in temperature of the gas, thus reducing I the velocities attained in the lift. Moreover, because of the rapid heat exchange between solids and gas, the effect of reduction in gas temperature is realized in the lower portion of the lift and in the region more likely to be susceptible otherwise to conditions of unstable flow. The

effect of heat exchange between the hotter gas and the cooler catalyst is thus beneficially utilized in those regions of the lift where it may be most needed for stabilization of solids flow.

While the application of the invention has been principally described in connection with systems employing I lift conduits of substantially uniform diameter throughout, the invention is not limited thereto. Where the lift conduit is uniformly tapered through substantially its entire length by as much as one inch (diameter) per 25 feet of height, the use of lift gas having a temperature of 100 F. or more higher than that of the catalyst offers less advantage than it does in a straight lift. The process of the invention may be employed, to substantial, advantage, however, in systems wherein the overall taper is comparatively slight, such as those in which the over-all taper is less than about one inch in 40-50 feet. Morefrom the combined effects to obtain or more closely approach substantially uniform velocities throughout the entire lift height above the small lower portion thereof wherein the catalyst is accelerated to the desired velocity.

I claim as my invention: l. ina hydrocarbon conversion process in which hot granular contact material gravitates through a d'ownfiow path, including at least one contact zoneiwhereinv said granular material is contacted with gaseous material, and in which said granular material is withdrawn from said downflow path and elevated through a confined lift path out of heat exchange relation with said downflow path tainscarbon monoxide and said heating isefiected by the exothermic heat resulting from oxidation of said carbon by lift gas comprising gaseous efiiuent withdrawn from i one of said contact zones at a pressure lower than the desired operating pressure at the bottom of said lift path, the improvement which comprises the steps of: injecting steam at high velocity into said withdrawn gaseous effluent to pressurize the same sufliciently to supply the resultant gaseous mixture to said lift path at said operating pres:

sure, and heating said gaseous mixture to a temperature at least equal to the temperature of said withdrawn granular material before supplying said gaseous mixture to said lift path, thereby preventing such heat exchange between said granular material and said gaseous mixture within said lift path as would effect any substantial'decrease in the density of said lift gas.

2. A method as in claim 1 in which at least a portion of said heat is supplied to said gaseous mixture by introducing said pressurizing steam in superheated condition to said gaseous effluent.

3. A method as in claim 1 in-which said heating of the gaseous mixture is effected in a separate heating zone.

method asinclaim 3 in which said eflluentvconmonoxide to carbondioxide. 1

5. A method as in claim =1 in which-said ma granular material is, at a temperature in the range of about 800 llO0 F., and said gaseous mixture is supplied as lift gas to said lift path at a temperature'in thetrangc I ofabout 400 F. higher than the temperature of said i withdrawn granular material.

6. A methodasin claim4 in which said temperature I of the gaseous, mixture is in the range of about 200-350 F. higher than the temperature of said granular material.

References Cited in the file of this patent i Q 

1. IN A HYDROCARBON CONVERSION PROCESS IN WHICH HOT GRANULAR CONTACT MATERIAL GRAVITATES THROUGH A DOWNFLOW PATH, INCLUDING AT LEAST ONE CONTACT ZONE WHEREIN SAID GRANULAR MATERIAL IS CONTACTED WITH GASEOUS MATERIAL, AND IN WHICH SAID GRANULAR MATERIAL IS WITHDRAWN FROM SAID DOWNFLOW PATH AND ELEVATED THROUGH A CONFINED LIFT PATH OUT OF HEAT EXCHANGE RELATION WITH SAID DOWNFLOW PATH BY LIFT GAS COMPRISING GASEOUS EFFLUENT WITHDRAW FROM ONE OF SAID CONTACT ZONES AT A PRESSURE LOWER THAN THE DESIRED OPERATING PRESSURE AT THE BOTTOM OF SAID LIFT PATH. THE IMPROVEMENT WHICH COMPRISES THE STEPS OF: INJECTING STEAM AT HIGH VELOCITY INTO SAID WITHDRAWN GASEOUS EFFLUENT TO PRESSURIZED THE SAME SUFFICIENTLY TO SUPPLY THE RESULTANT 